This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Intellectual Merit: The Pacific-North America plate boundary in southern California is one of the only examples of recorded subduction of an oceanic spreading center in geological history, but this process is likely to be a common component of Earth history. Almost half of the Pacific-North America plate boundary in southern California lies offshore, but little is known about the physical properties of the oceanic plate, its mode of deformation, or its influence on western North America. This project will deploy 24 long-duration, broadband Ocean Bottom Seismometers (OBS) in a passive seismic experiment off the coast of southern California that spans the oceanic half of the Pacific-North America plate boundary. The OBS data will be combined with same-event data recorded on the permanent California Integrated Seismic Network for coverage across the onshore basins, San Andreas fault, and into the North America plate. The objective is to understand the tectonic interaction at this boundary by identifying the physical properties and deformation styles of the Pacific plate and near-shore microplates, as well as distinguish among contrasting upper mantle geodynamic scenarios which predict large-scale mantle flow patterns beneath western North America. The seismic studies aim to characterize the driving plate motion consequences of collision between the rift system, a fragmented subducted plate, the lengthening of the San Andreas transform fault system, and block rotations. Of particular relevance is understanding the source of the forces and rheology that affect the stress state of the elastic crust to generate earthquakes. The boundaries for the seismic array overlap the region of complex breakup and fracture of the Pacific plate near-shore where several microplates are observed, and extends far to the west to provide comparison with oceanic lithosphere that is not fractured and has formed at a uniform rate. The results will aid in understanding the boundary forces due to relative plate motions, the driving forces and characteristics of oceanic and continental scale deformation, and how the continental margin accretionary process is influenced by offshore tectonics. An additional goal is to examine the local earthquake data and their focal mechanisms for seismicity patterns. The local seismicity recorded by the proposed OBS network is expected to produce a more accurate offshore hypocenter catalog that can be used to identify spatial relationships between background seismic activity with mapped offshore faults
Broader Impacts: The broader impacts will be carried out through activities that include a partnership with the Southern California Marine Institute to create hands-on scientific opportunities and educational materials. These materials will incorporate the OBS data and general offshore seismology into programs for high school and college students. Undergraduate and graduate students will participate in the research cruises, scientific analysis, and related teaching activities. Masters and undergraduate level students from Cal State Northridge, a designated Minority Serving Institution, will include women and minority students through the Catalyst program which recruits actively for minorities in geology and geophysics. Data from the experiment will be archived at the IRIS Data Management Center and the Southern California Earthquake Data Center, both of which are multi-user data archival facilities that are open to data requests from other scientists, students, and non-scientists. The local earthquake data collection portion of this experiment will enhance the understanding of hazardous offshore seismic structures in applications that can directly benefit society. The offshore background seismicity catalog will elucidate the activity of offshore faults. Local earthquake phase data will contribute to an updated 3D crustal seismic velocity model that extends offshore to be used by researchers to carry out 3D wave propagation simulations to estimate the amount and effects of shaking on nearby coastal communities for use in mitigation efforts.
